This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A majority of the population believes in the benefits of nutritional supplements and takes them regularly. Understanding how different components of supplements interact and the mechanisms of their effects are vital for rational use and recommendations. The branched chain amino acids (BCAA) include leucine, isoleucine and valine and are unique in their effects on skeletal muscle and frequently used to reduce delayed onset muscle soreness and muscle fatigue after exercise. The objective of this work will be to determine whether BCAA and histidine (HIS) or B-alanine (B-ALA), which are precursors for camosine (CAR) synthesis, interact to enhance exercise performance. Carnosine is a dipetide composed of B-ALA and HIS and abundant in muscle and nervous tissue. We hypothesize that the addition of HIS or B-ALA to the BCAA regimen increases CAR levels, which in turn enhances the effectiveness of BCAA because of the CAR's antioxidant and buffering properties. A four-week supplementation period will be used to determine whether complementary effects exist between BCAA and HIS or B-ALA, leading to improved endurance (longer time to fatigue) and attenuation of muscle injury after prolonged low intensity exercise. This would support the concept that exercise performance may be enhanced by a combination of AA supplements. The mechanisms to be examined include the role of oxidative stress and the effect of the supplements on factors related to muscle synthesis and repair. This is of significance for athletes who want to enhance exercise performance and tolerance. Furthermore, the data will lay the groundwork for future studies in the older population for whom exercise tolerance and maintenance of body protein mass are essential to longevity and well-being.